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ANAT390 GI System
ANAT390 Lecture 27 GI System 2
What is the purpose of the stomach?
The stomach initiates digestion of food.
Describe the gastric mucosa.
Simple columnar epithelium
Gastric glands are found in the depressions of the epithelium
Apical/lumenal spithelial secretions are mucous, acid, and proteases
Basal secretions are hormones and paracrine factors
Transient gastric mucosal folds
How many sphincters are in the stomach and where are they located?
Lower Esophageal/Cardiac Sphincter
What are the six type of cells in the gastric epithelium?
surface lining cell
mucous neck cell
oxyntic (parietal cell)
zymogenic (chief) cell
What is the function of chief cells?
Secrete zymogens apically into the lumen
Zymogens are activated by acid hydrolysis
What is the function of enteroendocrine cells?
Secrete hormones and paracrine factors
ie. Vasoactive Intestinal Peptide (VIP) - increases peristalsis of intestines
Gastrin - increases parietal cell acid secretion in stomach and relaxes pyloric sphincter
What is the function of the small intestine?
Digestive- via enzymes delivered to the small intestine from the pancreas
Absorptive - via mucosa
Describe the layers of the small intestine.
Epithelium - simple columnar, absorptive cells (Enterocytes), protective mucous secreting goblet cells, anti-bacterial paneth cells
Lamina Propria - Loose connective tissue, many vascular capillaries and lymphatic capillaries (central lacteals), prominent MALT
Submucosa - alkaline, mucous secreting 'Brunner's Glands'
How does the small intestine increase its absorptive surface area?
Makes use of microvilli (projections) and crypts/glands (depressions)
Microvilli contain many channels/transporters in plasma membranes
What are paneth cells?
Contain apical pink/eosinophilic granules
Secrete antibacterial lysosymes
Can become phagocytic, antigen-presenting cells
What are Brunner's Glands?
Exocrine, secretory glands found in the submucosa all the way to the muscularis mucosa
Secrete protective, alkaline mucous which is protective of acid produced by the stomach
Ducts empty into base of intestinal crypts
Describe the MALT in the small intestine.
B and T Cell aggregates (no CT capsule)
Can be activated by Paneth cell-mediated Antigen Presentation
Pale germinal centers indicate B Cell Activation
Increase in numbers towards the terminal end of the small intestine
In appendix (at small/large intestinal junction, fill entire lamina propria)
Describe the layers of the large intestine.
: Absorptive (especially for H2O), crypts/glands present, but no villi
: Simple columnar; enterocytes with high number of goblet cells
: no brunner's glands
: Terminal thickenings= Anal Sphincters, smooth muscle internally and skeletal muscle externally
Describe the junction of the terminal portion of colon with the anus.
There is an epithelial transition between columnar epithelium and stratified squamous epithelium.
The pectinate line is the interface between endoderm and ectoderm.
Metaplasia can occur here as well.